Toward a standardized procedure for charcoal analysis

Sedimentary charcoal records are used for understanding fire as an earth system process, however, no standardized laboratory methodology exists. Varying sample volumes and chemical treatments (i.e. type of chemical for length of time) are used for the deffloculation and extraction of charcoal from sediment samples. Here, we present the first systematic assessment of the effect of commonly used chemicals on charcoal area and number of fragments. In modern charcoal the area of fragments was significantly different depending on the chemical treatment. We subsequently applied H₂O₂ (33%), NaClO (12.5%) and HNO₃ (50%) to a late-glacial-early Holocene palaeorecord and tested different sample volumes. The effects of the treatments were consistent between modern and fossil experiments, which demonstrates the validity of applying results from the modern experiment to the fossil records. Based on our experiments we suggest i) H₂O₂ 33%, especially for highly organic sediments; ii) avoidance of high concentrations of NaClO for prolonged periods of time, and HNO₃; and iii) samples of 1cm³ provided typically consistent profiles. Our results indicate that charcoal properties can be influenced by treatment type and sample volume, thus emphasizing the need for a common protocol to enable reliable multi-study comparisons or composite fire histories.